Method and system for providing a diluted free layer magnetic junction usable in spin transfer torque applications

ABSTRACT

A magnetic junction and method for providing the magnetic junction are described. The magnetic junction resides on a substrate and is usable in a magnetic device. The magnetic junction includes free and pinned layers separated by a nonmagnetic spacer layer. The free layer is switchable between stable magnetic states when a write current is passed through the magnetic junction. The free layer has a free layer perpendicular magnetic anisotropy energy greater than a free layer out-of-plane demagnetization energy. The free layer also includes a diluted magnetic layer having an out-of-plane demagnetization energy and a perpendicular magnetic anisotropy greater than the out-of-plane demagnetization energy. The diluted magnetic layer includes at least one magnetic material and at least one nonmagnetic material. The diluted magnetic layer has an exchange stiffness that is at least eighty percent of an exchange stiffness for the magnetic material(s).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional Patent ApplicationSer. No. 62/405,595, filed Oct. 7, 2016, entitled STT-MRAM SWITCHINGIMPROVEMENT BY FREE LAYER DILUTION WITHOUT EXCHANGE STIFFNESS REDUCTION,assigned to the assignee of the present application, and incorporatedherein by reference.

BACKGROUND OF THE INVENTION

Magnetic memories, particularly magnetic random access memories (MRAMs),have drawn increasing interest due to their potential for highread/write speed, excellent endurance, non-volatility and low powerconsumption during operation. An MRAM can store information utilizingmagnetic materials as an information recording medium. One type of MRAMis a spin transfer torque random access memory (STT-MRAM). STT-MRAMutilizes magnetic junctions written at least in part by a current driventhrough the magnetic junction. A spin polarized current driven throughthe magnetic junction exerts a spin torque on the magnetic moments inthe magnetic junction. As a result, layer(s) having magnetic momentsthat are responsive to the spin torque may be switched to a desiredstate.

For example, a conventional magnetic tunneling junction (MTJ) may beused in a conventional STT-MRAM. The conventional MTJ typically resideson a substrate. The conventional MTJ, uses conventional seed layer(s),may include capping layers and may include a conventionalantiferromagnetic (AFM) layer. The conventional MTJ includes aconventional pinned layer, a conventional free layer and a conventionaltunneling barrier layer between the conventional pinned and free layers.A bottom contact below the conventional MTJ and a top contact on theconventional MTJ may be used to drive current through the conventionalMTJ in a current-perpendicular-to-plane (CPP) direction.

The conventional pinned layer and the conventional free layer aremagnetic. The magnetization of the conventional pinned layer is fixed,or pinned, in a particular direction. The conventional free layer has achangeable magnetization. The conventional free layer may be a singlelayer or include multiple layers.

To switch the magnetization of the conventional free layer, a current isdriven perpendicular to plane. When a sufficient current is driven fromthe top contact to the bottom contact, the magnetization of theconventional free layer may switch to be parallel to the magnetizationof a conventional bottom pinned layer. When a sufficient current isdriven from the bottom contact to the top contact, the magnetization ofthe free layer may switch to be antiparallel to that of the bottompinned layer. The differences in magnetic configurations correspond todifferent magnetoresistances and thus different logical states (e.g. alogical “0” and a logical “1”) of the conventional MTJ.

Because of their potential for use in a variety of applications,research in magnetic memories is ongoing. Mechanisms for improving theperformance of STT-MRAM are desired. For example, a lower switchingcurrent may be desired for easier and faster switching. Concurrently,the magnetic junction is desired to remain thermally stable.Accordingly, what is needed is a method and system that may improve theperformance of the spin transfer torque based memories. The method andsystem described herein address such a need.

BRIEF SUMMARY OF THE INVENTION

A magnetic junction and method for providing the magnetic junction aredescribed. The magnetic junction resides on a substrate and is usable ina magnetic device. The magnetic junction includes free and pinned layersseparated by a nonmagnetic spacer layer. The free layer is switchablebetween stable magnetic states when a write current is passed throughthe magnetic junction. The free layer has a free layer perpendicularmagnetic anisotropy energy greater than a free layer out-of-planedemagnetization energy. The free layer also includes a diluted magneticlayer having an out-of-plane demagnetization energy and a perpendicularmagnetic anisotropy greater than the out-of-plane demagnetizationenergy. The diluted magnetic layer includes at least one magneticmaterial and at least one nonmagnetic material. The diluted magneticlayer has an exchange stiffness that is at least eighty percent of anexchange stiffness for the magnetic material(s).

The magnetic junction having the diluted magnetic layer in the freelayer may have improved performance. The diluted magnetic layer may havea reduced magnetic moment and increased thickness while substantiallymaintaining the exchange stiffness. As a result, switching performancemay be improved.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 depicts an exemplary embodiment of a magnetic junction usable ina magnetic devices such as a magnetic memory programmable using spintransfer torque and having a free layer including a diluted magneticlayer.

FIG. 2 depicts an exemplary embodiment of a free layer usable in amagnetic junction and including a diluted magnetic layer.

FIG. 3 depicts another exemplary embodiment of a free layer usable in amagnetic junction and including a diluted magnetic layer.

FIG. 4 depicts another exemplary embodiment of a magnetic junctionusable in a magnetic devices such as a magnetic memory programmableusing spin transfer torque and having a free layer including a dilutedmagnetic layer.

FIG. 5 depicts another exemplary embodiment of a magnetic junctionusable in a magnetic devices such as a magnetic memory programmableusing spin transfer torque and having a free layer including a dilutedmagnetic layer.

FIG. 6 is a flow chart depicting an exemplary embodiment of a method forproviding a magnetic junction usable in a magnetic devices such as amagnetic memory programmable using spin transfer torque and having afree layer including a diluted magnetic layer.

FIG. 7 is a flow chart depicting an exemplary embodiment of a method forproviding a free layer including a diluted magnetic layer.

FIG. 8 depicts an exemplary embodiment of a memory utilizing magneticjunctions in the memory element(s) of the storage cell(s).

DETAILED DESCRIPTION OF THE INVENTION

The exemplary embodiments relate to magnetic junctions usable inmagnetic devices, such as magnetic memories, and the devices using suchmagnetic junctions. The magnetic memories may include spin transfertorque magnetic random access memories (STT-MRAMs) and may be used inelectronic devices employing nonvolatile memory. Such electronic devicesinclude but are not limited to cellular phones, smart phones, tables,laptops and other portable and non-portable computing devices. Thefollowing description is presented to enable one of ordinary skill inthe art to make and use the invention and is provided in the context ofa patent application and its requirements. Various modifications to theexemplary embodiments and the generic principles and features describedherein will be readily apparent. The exemplary embodiments are mainlydescribed in terms of particular methods and systems provided inparticular implementations. However, the methods and systems willoperate effectively in other implementations. Phrases such as “exemplaryembodiment”, “one embodiment” and “another embodiment” may refer to thesame or different embodiments as well as to multiple embodiments. Theembodiments will be described with respect to systems and/or deviceshaving certain components. However, the systems and/or devices mayinclude more or less components than those shown, and variations in thearrangement and type of the components may be made without departingfrom the scope of the invention. The exemplary embodiments will also bedescribed in the context of particular methods having certain steps.However, the method and system operate effectively for other methodshaving different and/or additional steps and steps in different ordersthat are not inconsistent with the exemplary embodiments. Thus, thepresent invention is not intended to be limited to the embodimentsshown, but is to be accorded the widest scope consistent with theprinciples and features described herein.

A magnetic junction and method for providing the magnetic junction aredescribed. The magnetic junction resides on a substrate and is usable ina magnetic device. The magnetic junction includes free and pinned layersseparated by a nonmagnetic spacer layer. The free layer is switchablebetween stable magnetic states when a write current is passed throughthe magnetic junction. The free layer has a free layer perpendicularmagnetic anisotropy energy greater than a free layer out-of-planedemagnetization energy. The free layer also includes a diluted magneticlayer having an out-of-plane demagnetization energy and a perpendicularmagnetic anisotropy greater than the out-of-plane demagnetizationenergy. The diluted magnetic layer includes at least one magneticmaterial and at least one nonmagnetic material. The diluted magneticlayer has an exchange stiffness that is at least eighty percent of anexchange stiffness for the magnetic material(s).

The exemplary embodiments are described in the context of particularmethods, magnetic junctions and magnetic memories having certaincomponents. One of ordinary skill in the art will readily recognize thatthe present invention is consistent with the use of magnetic junctionsand magnetic memories having other and/or additional components and/orother features not inconsistent with the present invention. The methodand system are also described in the context of current understanding ofthe spin transfer phenomenon, of magnetic anisotropy, and other physicalphenomenon. Consequently, one of ordinary skill in the art will readilyrecognize that theoretical explanations of the behavior of the methodand system are made based upon this current understanding of spintransfer, magnetic anisotropy and other physical phenomena. However, themethod and system described herein are not dependent upon a particularphysical explanation. One of ordinary skill in the art will also readilyrecognize that the method and system are described in the context of astructure having a particular relationship to the substrate. However,one of ordinary skill in the art will readily recognize that the methodand system are consistent with other structures. In addition, the methodand system are described in the context of certain layers beingsynthetic and/or simple. However, one of ordinary skill in the art willreadily recognize that the layers could have another structure.Furthermore, the method and system are described in the context ofmagnetic junctions and/or substructures having particular layers.However, one of ordinary skill in the art will readily recognize thatmagnetic junctions and/or substructures having additional and/ordifferent layers not inconsistent with the method and system could alsobe used. Moreover, certain components are described as being magnetic,ferromagnetic, and ferrimagnetic. As used herein, the term magneticcould include ferromagnetic, ferrimagnetic or like structures. Thus, asused herein, the term “magnetic” or “ferromagnetic” includes, but is notlimited to ferromagnets and ferrimagnets. As used herein, “in-plane” issubstantially within or parallel to the plane of one or more of thelayers of a magnetic junction. Conversely, “perpendicular” and“perpendicular-to-plane” corresponds to a direction that issubstantially perpendicular to one or more of the layers of the magneticjunction. The method and system are also described in the context ofcertain alloys. Unless otherwise specified, if specific concentrationsof the alloy are not mentioned, any stoichiometry not inconsistent withthe method and system may be used. For example, CoFeB and FeV refer to acobalt-iron boron alloy and an iron-vanadium alloy, respectively, thatmay be within the stoichiometry ranges described herein. Thus, the useof CoFeB and FeV are not intended to indicate that the alloys areequiatomic.

FIG. 1 depicts an exemplary embodiment of a magnetic junction 100 usablein a magnetic devices such as a magnetic memory programmable using spintransfer torque and having a free layer including a diluted magneticlayer. For clarity, FIG. 1 is not to scale. The magnetic junction 100may be used in a magnetic device such as a spin transfer torque magneticrandom access memory (STT-MRAM) and, therefore, in a variety ofelectronic devices. The magnetic junction 100 may include a pinned layer104 having a magnetic moment 105, a nonmagnetic spacer layer 106, a freelayer 108 having magnetic moment 109, an optional additional nonmagneticspacer layer 110, and an optional additional pinned layer 112 havingmagnetic moment 113. The magnetic junction 100 may also include one ormore polarization enhancement layers (PELs) 103, 107 and 111. In otherembodiments, some or all of the PELs 103, 107 and 111 may be omitted oradditional PELs may be employed. Also shown are optional seed layer(s)102 and capping layer(s) 114. The substrate 101 on which the magneticjunction 100 is formed resides below the seed layers. A bottom contactand a top contact are not shown but may be formed. Similarly, otherlayers may be present but are not shown for simplicity.

As can be seen in FIG. 1, the magnetic junction 100 is a dual magneticjunction. In another embodiment, the nonmagnetic spacer layer 110 andpinned layer 112 might be omitted. In such an embodiment, the magneticjunction 100 is a bottom pinned magnetic junction. Alternatively, thepinned layer 104 and nonmagnetic spacer layer 106 might be omitted. Insuch an embodiment, the magnetic junction 100 is a top pinned magneticjunction. Optional pinning layer(s) (not shown) may be used to fix themagnetization of the pinned layer(s) 104 and/or 112. In someembodiments, the optional pinning layer may be an AFM layer ormultilayer that pins the magnetization(s) through an exchange-biasinteraction. However, in other embodiments, the optional pinning layermay be omitted or another structure may be used. In the embodimentshown, the magnetic moments 105 and 113 of the pinned layers 104 and112, respectively, are pinned by the magnetic anisotropy of the layers104 and 112, respectively. The free layer 108 and the pinned layers 104and 112 have a high perpendicular magnetic anisotropy. Stateddifferently, the perpendicular magnetic anisotropy energy exceeds theout-of-plane demagnetization energy for the layers 104, 108 and 112.Such a configuration allows for the magnetic moments 105, 109 and 113 ofthe layers 104, 108 and 112, respectively, having a high perpendicularmagnetic anisotropy to be stable perpendicular to plane. Stateddifferently, the magnetic moments of the free layer 108 and pinnedlayer(s) 104 and 112 are stable out-of-plane.

The magnetic junction 100 is also configured to allow the free layermagnetic moment 109 to be switched between stable magnetic states when awrite current is passed through the magnetic junction 100. Thus, thefree layer 109 is switchable utilizing spin transfer torque when a writecurrent is driven through the magnetic junction 100 in a currentperpendicular-to-plane (CPP) direction. The direction of the magneticmoment 109 of the free layer 108 may be read by driving a read currentthrough the magnetic junction 100.

The nonmagnetic spacer layer(s) 106 and 110 may be tunneling barrierlayers. For example, the nonmagnetic spacer layer 106 and/or 110 may bea crystalline MgO tunneling barrier with a (100) orientation. Suchnonmagnetic spacer layers 106 and 110 may enhance TMR of the magneticjunction 100. The nonmagnetic spacer layer(s) 106 and 110 may also beconsidered to serve as seed and capping layers for the free layer 108.

The pinned layer(s) 104 and/or 112 have a perpendicular magneticanisotropy energy greater than a pinned layer out-of-planedemagnetization energy. Thus, the moments 105 and 113 are stableperpendicular-to-plane. In alternate embodiments, the magnetic moment(s)105 and/or 113 may be stable in-plane. The pinned layers 104 and 112 areshown as being simple, single layers. However, in other embodiments, thepinned layer(s) 104 and/or 112 may be multilayer(s). For example, thepinned layer(s) 104 and/or 112 might be a synthetic antiferromagnet(SAF) including two magnetically coupled ferromagnetic layers separatedby and sandwiching a nonmagnetic layer, such as Ru. Alternatively, thepinned layer(s) 104 and/or 112 may be high perpendicular anisotropy(H_(k)) multilayer(s). For example, the pinned layer 104 may be a Co/Ptmultilayer. Other pinned layer(s) having other structures may be used.In addition, in alternate embodiments, the pinned layer 102 and/or 112may have the magnetic moment(s) 105 and/or 113, in plane.

The free layer 108 includes at least one diluted magnetic layer. Adiluted magnetic layer includes one or more magnetic materials alloyedwith one or more nonmagnetic materials. The magnetic material(s) arediluted by the nonmagnetic material(s). Because magnetic material(s) arealloyed with nonmagnetic material(s), the saturation magnetization ofthe diluted magnetic layer is less than the saturation magnetization ofthe magnetic material(s) only. Such a decrease in magnetization may bedue to one or more factors. The magnetic substitutional effect occurswhen a nonmagnetic atoms substitutes for a magnetic atom in the lattice.Because fewer magnetic atoms are present in a given amount of material,the saturation magnetic moment is reduced. The volume of a given amountof material may be increased or decreased in the alloy. For example, alarge nonmagnetic atom is used in the alloy, the volume of the materialper unit cell may be increased. This may reduce the saturationmagnetization. In addition, the induced magnetic moment of the magneticatoms may be reduced due to a change in the electronic interaction.Thus, for various reasons, the saturation magnetization of the dilutedmagnetic layer is reduced.

Typically, such a dilution of the magnetic material(s) and reduction ofsaturation magnetization also dramatically reduces the exchangestiffness of the magnetic layer. However, in the free layer 108, theexchange stiffness(es) of the diluted magnetic layer(es) aresubstantially maintained. More specifically, the exchange stiffness ofthe diluted magnetic layer is at least eighty percent of an exchangestiffness for the magnetic material(s). In some embodiments, theexchange stiffness of the diluted magnetic layer is at least ninetypercent of the exchange stiffness for the magnetic material(s). In somesuch embodiments, the exchange stiffness of the diluted magnetic layeris at least ninety-five percent of the exchange stiffness for themagnetic material(s). For some concentrations of the nonmagneticmaterial(s), the exchange stiffness of the diluted magnetic layer isunchanged or increased from that of the magnetic material(s) despite thereduction in saturation magnetization. In general, the Curie temperatureof the alloy for the diluted magnetic layer varies with the exchangestiffness. Thus, the Curie temperature of the diluted magnetic layer maybe at least eighty percent of the Curie temperature(s) of the magneticmaterial(s). In some embodiments, the Curie temperature of the dilutedmagnetic layer is at least ninety percent of the Curie temperature(s)for the magnetic material(s). In some such embodiments, the Curietemperature of the diluted magnetic layer is at least ninety-fivepercent of the Curie temperature(s) for the magnetic material(s). Forsome concentrations of the nonmagnetic material(s), the Curietemperature of the diluted magnetic layer is unchanged or increased fromthat of the magnetic material(s).

The diluted magnetic layer has a perpendicular magnetic anisotropyenergy that is greater than its out-of-plane demagnetization energy.Thus, the magnetization of the diluted magnetic layer may beperpendicular-to-plane. Because the saturation magnetization of thediluted magnetic layer is reduced, the demagnetization field of thediluted magnetic layer is also reduced. Consequently, the dilutedmagnetic layer may also be made thicker while maintaining theperpendicular-to-plane magnetic moment. The free layer 108 may also bemade thicker for the same reasons. For example, the free layer 108 mayhave a thickness of at least twenty Angstroms and not more thanthirty-five Angstroms. The diluted magnetic layer may have a thicknessof at least twelve Angstroms and not more than twenty-two Angstroms insuch a free layer. In other embodiments, the diluted magnetic layer mayhave a thickness of at least twenty Angstroms and not more thanthirty-five Angstroms.

Examples of materials that may be used in the diluted magnetic layerinclude Fe as the magnetic material and at least one of V, Mo, Cr, Al,Ga, W, Sb, Ge and Sn as the nonmagnetic material(s) in the alloy.Alloying Fe with these nonmagnetic materials results in a dilution ofthe Fe magnetic moment and, therefore, a reduced saturationmagnetization. In addition, the diluted magnetic layer may have anexchange stiffness that is not substantially reduced for someconcentrations. For example, the diluted magnetic layer that includes Femay include at least one of at least ten atomic percent and not morethan twenty-five atomic percent V, greater than zero and not more thanfive atomic percent Mo, greater than zero and not more than ten atomicpercent Cr, greater than zero and not more than twenty atomic percentAl, greater than zero and not more than twenty atomic percent Ga,greater than zero and not more than ten atomic percent W, greater thanzero and not more than ten atomic percent Sb, greater than zero and notmore than ten atomic percent Ge and greater than zero and not more thanten atomic percent Sn. In some embodiments, the diluted magnetic layermay consist of FeX and wherein X is at least ten atomic percent and notmore than twenty-five atomic percent V, greater than zero and not morethan five atomic percent Mo, greater than zero and not more than tenatomic percent Cr, greater than zero and not more than twenty atomicpercent Al, greater than zero and not more than twenty atomic percentGa, greater than zero and not more than ten atomic percent W, greaterthan zero and not more than ten atomic percent Sb, greater than zero andnot more than ten atomic percent Ge or greater than zero and not morethan ten atomic percent Sn. For example, the diluted magnetic layer is aFe_(1-t)V_(t) layer wherein t is at least 0.1 and not more than 0.25.

The free layer 108 may be a multilayer including other layers. Forexample, the free layer 108 may also include CoFeB layer(s) and/or Felayer(s) adjoining the diluted magnetic layer. In some embodiments, theCoFeB includes at least ten atomic percent and not more than sixtyatomic percent B (i.e. Co_(x)Fe_(y)B_(z) where x+y+z=1 and z is at least0.1 and not more than 0.6). In some such embodiments, the CoFeB includesat least fifteen percent and not more than forty atomic percent B. Thefree layer 108 might also include multiple diluted magnetic layers.

The layers surrounding the free layer 108 may be tailored to aid thefree layer 108 and diluted magnetic layer in maintaining a highperpendicular magnetic anisotropy. For example, a seed layer and/orcapping layer may be selected from a set of materials in order toenhance the perpendicular magnetic anisotropy energy. In someembodiments, such a seed layer may include magnesium oxide. Similarly,the capping layer be a magnesium oxide layer. For example, in the dualmagnetic junction 100 depicted in FIG. 1, the nonmagnetic spacers 106and 110 may each be crystalline MgO tunneling barrier layers. Thus, theseed and capping layers would correspond to the nonmagnetic spacerlayers 106 and 110, respectively and may consist of MgO. Suchnonmagnetic spacer layers 106 and 110 not only improve tunnelingmagnetoresistance, but may also aid in increasing the perpendicularmagnetic anisotropy of the free layer 108. If the layers 110 and 112 areomitted, then the capping layer 114 may include a magnesium oxide layer.It the layers 104 and 106 are omitted, then the seed layer 102 mayinclude magnesium oxide. Other material(s) may be used for the seedlayer 102 and capping layer 114 to improve the perpendicular magneticanisotropy of the free layer 108. Thus, the free layer magnetic moment109 may have its stable states substantially perpendicular-to-plane.

The magnetic junction 100 having the free layer 108 including a dilutedmagnetic layer may have improved performance. The free layer 108 mayhave a reduced saturation magnetization due to the dilution of themagnetic moment. For example, saturation magnetizations below 1000emu/cc (as compared to a bulk Fe saturation magnetization ofapproximately 1800 emu/cc) may be obtained. For some materials, such asV, significantly lower saturation magnetizations may be achieved in theconcentration ranges described above. However, the exchange stiffnessmay be maintained. As a result, a thicker free layer 108 may beobtained. In some embodiments, such as those using nonmagnetic materialsV, Mo, Cr, Al, Ga, Sb, Ge and/or Sn with Fe, low damping may bemaintained. As a result, switching current may be reduced. The reductionin switching current may also improve other aspects of performance, suchas switching speed. Thus, performance of the magnetic junction 100 andmagnetic device employing such a free layer 108 may be enhanced.

FIG. 2 depicts an exemplary embodiment of a free layer 120 usable in amagnetic devices such as a magnetic memory programmable using spintransfer torque. For clarity, FIG. 2 is not to scale. The free layer 120may be used as the free layer 108 in the magnetic junction 100. The freelayer 120 includes a CoFeB or Fe layer 122, a diluted magnetic layer 124and an additional Fe or CoFeB layer 126. In some embodiments, thelayer(s) 122 and/or 126 may be omitted. However, in some instances, theinterface of the diluted magnetic layer 124 coinciding with theinterface of the free layer 120 may reduce the perpendicular magneticanisotropy of the free layer 120. In such instances, the dilutedmagnetic layer 124 is desired to be surrounded by other magnetic layers122 and 126. Also shown are seed layer(s) 131 and capping layer(s) 132.However, these layers 131 and 132 are not considered part of the freelayer 120.

The diluted magnetic layer 124 is analogous to that described above.Consequently, the diluted magnetic layer 124 may have a lower saturationmagnetization, a substantially preserved exchange stiffness and may bethicker. Thus, the exchange stiffness of the diluted magnetic layer 124is at least eighty percent of an exchange stiffness for the magneticmaterial(s). In some embodiments, the exchange stiffness of the dilutedmagnetic layer 124 is at least ninety percent of the exchange stiffnessfor the magnetic material(s). For some concentrations of the nonmagneticmaterial(s), the exchange stiffness of the diluted magnetic layer isunchanged or increased from that of the magnetic material(s). Forexample, if the diluted magnetic layer 124 is an Fe_(1-t)V_(t) layer,where t is at least 0.1 and not more than 0.25, then the exchangestiffness of the diluted magnetic layer 124 may be at least that of Fe.The Curie temperature of the diluted magnetic layer 124 may vary in ananalogous manner.

The diluted magnetic layer 124 and the free layer 120 each has aperpendicular magnetic anisotropy that exceeds the out-of-planedemagnetization energy. Thus, the free layer magnetic moment 121 mayhave its stable states substantially perpendicular-to-plane. In someembodiments, the high perpendicular magnetic anisotropy of the freelayer 120 may be due at least in part to the layers 122 and 126. This isbecause some diluted magnetic layers 124 may have a reducedperpendicular magnetic anisotropy at interfaces with certain otherlayers, such as MgO tunneling barrier layers. For example, an FeVdiluted magnetic layer may have reduced perpendicular magneticanisotropy due to such interfaces with MgO. In such embodiments, thelayers 122 and/or 126 are desired to be present. Such layers may aid inmaintaining the perpendicular magnetic anisotropy of the dilutedmagnetic layer 124 and, therefore, the free layer 120. The free layer120 and the diluted magnetic layer 124 may have a thickness as describedabove. Thus, in some embodiments, the thickness of the diluted magneticlayer 122 may be greater than twenty Angstroms and not more thanthirty-two Angstroms while maintaining a perpendicular-to-plane magneticmoment. Similarly, the free layer 120 may have a thickness of at least(or greater than) twenty Angstroms and not more than thirty-fiveAngstroms while maintaining the perpendicular-to-plane magnetic moment121.

The bottom layer 122 may be CoFeB or Fe. In some embodiments, the layer122 is a CoFeB layer having the stoichiometry described above. The layer122 may also be desired to be thin. In some embodiments, the CoFeB layeror Fe layer 124 is also at least three Angstroms thick and not more thanten Angstroms thick. Similarly, the top layer 126 may be Fe or CoFeBhaving the stoichiometry described above. In some embodiments, thebottom layer 122 is a CoFeB layer while the top layer 126 is a Fe layer.The top layer 126 is also desired to be thin. In some embodiments, thelayer 126 is not more than five Angstroms thick.

In addition, the layers surrounding the free layer 120 may be tailoredto aid the layers 122, 124 and 126 and the free layer 120 in maintaininga high perpendicular magnetic anisotropy. For example, the seed layer131 may include a magnesium oxide layer. Similarly, the capping layer132 may include a magnesium oxide layer. Other material(s) may be usedto improve the perpendicular magnetic anisotropy of the free layer 120.The material selected may depend upon the type of magnetic junction(dual, bottom pinned or top pinned) and the location of the free layer120.

A magnetic junction including the free layer 120 may have improvedperformance. The free layer 120 may have a reduced saturationmagnetization due to the low moment of the diluted magnetic layer 124.However, the high perpendicular magnetic anisotropy and exchangestiffness may be maintained. The diluted magnetic layer 124 may alsohave low damping. As a result, switching current may be reduced. Theperpendicular magnetic anisotropy may remain high. Thus, performance ofa magnetic junction and magnetic device employing such a free layer 120may be improved.

FIG. 3 depicts another exemplary embodiment of a free layer 120′ usablein magnetic devices such as a magnetic memory programmable using spintransfer torque. For clarity, FIG. 3 is not to scale. The free layer120′ may be used as the free layer 108 in the magnetic junction 100. Thefree layer 120′ is analogous to the free layer 120. Consequently,similar components have analogous labels. The free layer 120′ includesan optional CoFeB or Fe layer 122, a diluted magnetic layer 124 and anoptional Fe or CoFeB layer 126. Also shown are seed layer(s) 131′ andcapping layer(s) 132′ that are analogous to the seed layer(s) 131 andthe capping layer(s) 132, respectively. However, these layers 131′ and132′ are not considered part of the free layer 120′.

In addition, the free layer 120′ may include one or more optionaldiffusion blocking layer(s) 123 and/or 125. The diffusion blockinglayers 123 and 125 may be used to prevent diffusion of the nonmagneticmaterial(s) in the diluted magnetic layer 124. For example, thediffusion blocking layers 123 and 125 may be configured to reduce orprevent diffusion of V from an FeV diluted magnetic layer 124. In someembodiments, only one of the layers 123 and 125 is present. However, inother embodiments, both layers 123 and 125 are used. For example,diffusion blocking layer(s) 123 and 125 may include one or more of Si,Cr, Nb, Re, Ti, Mo, As, Ru, W, Pd and Ta. The diffusion blocking layers123 and 125 may be sufficiently thin that the perpendicular magneticanisotropy, ability to be written using spin transfer torque andmagnetoresistance of the magnetic junction including the free layer 120′are maintained at a sufficient level for use in a device. The diffusionblocking layers 123 and 125 are also sufficiently thick that they areeffective in preventing the nonmagnetic material(s) of the dilutedmagnetic layer 124 in adversely affecting the remaining portion of thefree layer 120′ and magnetic junction. In some embodiments, thethickness of each of the diffusion blocking layers 123 and 125 may be atleast one Angstrom and not more than four Angstroms.

A magnetic junction including the free layer 120′ may have improvedperformance. The free layer 120′ may have a reduced saturationmagnetization due to the low moment of the diluted magnetic layer 124.However, the high perpendicular magnetic anisotropy and exchangestiffness may be maintained. The diluted magnetic layer 124 may alsohave low damping. As a result, switching current performance of amagnetic junction and magnetic device employing such a free layer 120′may be improved.

FIG. 4 depicts another exemplary embodiment of a magnetic junction 100′in magnetic devices such as a magnetic memory programmable using spintransfer torque. For clarity, FIG. 4 is not to scale. The magneticjunction 100′ is analogous to the magnetic junction 100. Consequently,similar components have analogous labels. The magnetic junction 100′ isa bottom pinned magnetic junction including optional polarizationenhancement layer 103, pinned layer 104, optional polarizationenhancement layer 107, nonmagnetic spacer layer 106 and free layer 108′that are analogous to the optional polarization enhancement layer 103,pinned layer 104, optional polarization enhancement layer 107,nonmagnetic spacer layer 106 and free layer 108, respectively. Optionalseed layer 102 and capping layer 114′ are also shown.

The free layer 108′ includes a diluted magnetic layer. In someembodiments, the free layer 108′ may be the free layer 120 or 120′. Inorder to improve the perpendicular magnetic anisotropy of the free layer108′, the nonmagnetic spacer layer 106 is desired to be a crystallineMgO layer. Thus, the nonmagnetic spacer layer 106 also serves as a seedlayer 131/131′. Such a crystalline MgO tunneling barrier layer 106 mayalso improve tunneling magnetoresistance and, therefore, signal from themagnetic junction 100′. The capping layers 114′ are desired to beanalogous to the layer(s) 132 and/or 132′. Thus, the capping layer(s)114′ may include a magnesium oxide layer.

The magnetic junction 100′ may have improved performance. The free layer108′ may have a reduced saturation magnetization due to the low momentof the diluted magnetic layer 124. However, the high perpendicularmagnetic anisotropy, exchange stiffness and out-of-plane magnetic moment109 may be maintained. The free layer 108′ may also have low damping andincreased thickness. As a result, switching performance of a magneticjunction 100′ and magnetic device employing the magnetic junction 100′may be improved.

FIG. 5 depicts another exemplary embodiment of a magnetic junction 100″in a magnetic devices such as a magnetic memory programmable using spintransfer torque. For clarity, FIG. 5 is not to scale. The magneticjunction 100″ is analogous to the magnetic junction(s) 100 and/or 100′.Consequently, similar components have analogous labels. The magneticjunction 100″ is a top pinned magnetic junction including free layer108′, nonmagnetic spacer layer 110, optional polarization enhancementlayer 111 and pinned layer 112 that are analogous to the free layer108/108′, nonmagnetic spacer layer 110, optional polarizationenhancement layer 111 and pinned layer 112, respectively. Optional seedlayer 102 and capping layer 114 are also shown.

The free layer 108′ includes a diluted magnetic layer. In someembodiments, the free layer 108′ may be the free layer 120 or 120′. Inorder to improve the perpendicular magnetic anisotropy of the free layer108′, the nonmagnetic spacer layer 110 is desired to be a crystallineMgO layer. Thus, the nonmagnetic spacer layer 110 also serves as acapping layer 132/132′. Such a crystalline MgO tunneling barrier layer110 may also improve tunneling magnetoresistance and, therefore, signalfrom the magnetic junction 100″. The seed layers 102′ are desired to beanalogous to the layer(s) 131 and/or 131′. Thus, the seed layer(s) 102′may include magnesium oxide.

The magnetic junction 100″ may have improved performance. The free layer108′ may have a reduced saturation magnetization due to the low momentof the diluted magnetic layer. However, the high perpendicular magneticanisotropy, exchange stiffness and out-of-plane magnetic moment 109 maybe maintained. The free layer 108′ may also have low damping andincreased thickness. As a result, switching current performance of amagnetic junction 100″ and magnetic device employing the magneticjunction 100″ may be improved.

Various features have been described with respect to the magneticjunctions 100, 100′ and 100″ and the free layers 18, 108′, 120 and 120′.One of ordinary skill in the art will recognize that these features maybe combined in manner(s) not shown and which are not inconsistent withthe devices and methods described herein.

FIG. 6 is a flow chart depicting an exemplary embodiment of a method 200for providing a layer for magnetic junction usable in a magnetic deviceand including a diluted magnetic layer within the free layer. Forsimplicity, some steps may be omitted, performed in another order,include substeps and/or combined. Further, the method 200 start afterother steps in forming a magnetic memory have been performed. The method200 is described in the context of the magnetic junction 100, 100′ and100″. However the method 200 may be used in forming other magneticjunction(s) and the free layers 120, 120′ and/or 120″. Further, multiplemagnetic junctions may be simultaneously fabricated.

Seed layer(s) 102 are provided on the substrate, via step 202. Step 202may include depositing the appropriate seed layer(s) for the pinnedlayer 104 or for the free layer 108. If the magnetic junction 100 or100′ is being fabricated, then the seed layer(s) for the pinned layer104 are provided in step 202. If the magnetic junction 100″ is beingfabricated, then the seed layer(s) 102 for the free layer 108/108′ areprovided in step 202. Thus, step 202 may include providing a magnesiumoxide layer.

In some embodiments, a polarization enhancement layer may be providedfor the pinned layer 104, via step 203. For example, step 203 mayinclude depositing a CoFeB layer. In other embodiments, step 203 may beomitted. A pinned layer 104 may be provided, via step 204. Step 204 isperformed if the entire dual magnetic junction 100 is to be formed or ifa bottom pinned magnetic junction 100′ that omits the layers 102 and 104is to be formed. Step 204 may include providing a multilayer structurehaving a high perpendicular magnetic anisotropy. Thus, the pinned layer104 formed in step 204 may be a simple (single) layer or may includemultiple layers. For example, the pinned layer formed in step 204 may bea synthetic antiferromagnet including magnetic layersantiferromagnetically or ferromagnetically coupled through thinnonmagnetic layer(s), such as Ru. Each magnetic layer may also includemultiple layers. In some embodiments, another polarization enhancementlayer may be provided on the pinned layer 104, via step 205. Forexample, step 205 may include depositing a CoFeB layer. In otherembodiments, step 205 may be omitted.

A nonmagnetic spacer layer 106 may be provided, via step 206. Step 206is performed if the dual magnetic junction 100 or a bottom pinnedmagnetic junction 100′ is to be formed. In some embodiments, acrystalline MgO tunneling barrier layer may be desired for the magneticjunction being formed. Step 206 may include depositing MgO using, forexample, radio frequency (RF) sputtering. In other embodiments, metallicMg may be deposited and then oxidized in step 206 to provide a naturaloxide of Mg. The MgO barrier layer/nonmagnetic spacer layer 106 may alsobe formed in another manner. Step 206 may include annealing the portionof the magnetic junction already formed to provide crystalline MgOtunneling barrier with a (100) orientation for enhanced TMR of themagnetic junction. Because the nonmagnetic spacer layer 106 may also beviewed as a seed layer for the free layer 108/108′, step 206 may also beseen as forming seed layer(s) 131 and/or 131′.

A free layer 108/108′ is provided, via step 208. Step 208 includesdepositing the material(s) for the free layer 108. If steps 204 and 206are omitted, then the free layer may be deposited on seed layer(s) instep 208. In such embodiments, a top pinned magnetic junction isfabricated. The seed layer(s) may be selected for various purposesincluding but not limited to the desired crystal structure and magneticproperties of the free layer 108/108′. For example, the free layer 108′may be provided on seed layer(s) 102′ such as a crystalline MgO layerthat promotes a perpendicular magnetic anisotropy in the free layer108/108′. If a dual magnetic junction or bottom pinned magnetic junctionis fabricated, the free layer may be formed on a nonmagnetic spacerlayer provided in step 206. Step 208 may also be viewed as providing thefree layer 120 or 120′. Thus, step 208 may include depositing one ormore layers including a diluted magnetic layer such as the layer 124.Multiple diluted magnetic layers may also be formed. A CoFeB layerand/or a Fe layer, such as the layer(s) 122 and/or 126, may also beprovided. Step 208 may also include cooling the layers that have beenprovided before depositing the free layer materials. For example, theportion of the magnetic junction 100 that has been deposited may becooled after step 206 and during step 208. Such a cooling step mayinclude placing the portion of the magnetic junction 100 that has beendeposited in a cooling chamber having a temperature less than roomtemperature (approximately twenty-three degrees Celsius). In someembodiments, the cooling chamber has a temperature of at least eightyKelvin and not more than three hundred Kelvin.

An additional nonmagnetic spacer layer 110 may be provided, via step210. Step 210 is performed if a dual magnetic junction 100 or a toppinned magnetic junction 100″ is desired to be fabricated. If a bottompinned magnetic junction is desired, then step 210 is omitted. In someembodiments, an additional crystalline MgO tunneling barrier layer maybe desired for the magnetic junction being formed. Step 210 may thus beperformed as described above with respect to step 206. For a dualmagnetic junction, the nonmagnetic spacer layer 110 may be considered tobe the main tunneling barrier layer. Thus, the thickness andcrystallinity of the layer 110 may be optimized in step 210.

In some embodiments, a polarization enhancement layer may be providedfor the pinned layer 112, via step 211. For example, step 211 mayinclude depositing a CoFeB layer. In other embodiments, step 211 may beomitted. An additional pinned 112 layer may optionally be provided, viastep 212. Step 212 may be performed if the dual magnetic junction 100 ortop pinned magnetic junction 100″ is desired to be fabricated. If abottom pinned magnetic junction 100′ is desired, then step 212 isomitted. The pinned layer 112 formed in step 212 may be a simple(single) layer or may include multiple layers. For example, the pinnedlayer formed in step 212 may be a SAF.

The capping layer(s) 114 may then be provided, via step 214. If thebottom pinned magnetic junction 100″ is being formed, then step 214 mayinclude providing a magnesium oxide layer. Step 214 may thus be seen asproviding the capping layer 132 or 132′ in some embodiments.

Fabrication of the magnetic junction 100 may then be completed. Forexample, the edges of the magnetic junction 100 may be defined. This maybe accomplished by providing a mask on the layers that have beendeposited and ion milling the exposed portions of the layers. In someembodiments, an ion mill may be performed. Thus, the edges of themagnetic junction 100 may be defined after steps 202 through 214 areperformed. Alternatively, the edges of various layers may be formed atother times. Additional structures, such as contacts and conductivelines may also be formed for the device in which the magnetic junctionis used.

Using the method 200, the magnetic junction 100, the magnetic junction100′ and/or the magnetic junction 100″ may be formed. The free layers108, 108′, 120 and/or 120′ may be fabricated. As a result, a magneticjunction having free layer(s) with improved switching characteristicsmay be achieved.

FIG. 7 is a flow chart depicting an exemplary embodiment of a method 220for providing a free layer for magnetic junction usable in a magneticdevice. The method 220 may be used to from the free layer 120 and/or120′. For simplicity, some steps may be omitted, performed in anotherorder, include substeps and/or combined. Further, the method 220 startafter other steps in forming a magnetic memory have been performed. Themethod 220 is described in the context of the free layers 120 and 120′.However the method 220 may be used in forming other free layer(s).Further, multiple free layers may be simultaneously fabricated.

A seed layer 131/131′ that adjoins, or shares an interface with, thefree layer 120 is provided, via step 222. In some embodiments, step 222includes depositing magnesium oxide. In some embodiments, the seed layerprovided in step 222 may form a nonmagnetic spacer layer of the magneticjunction being formed. Thus, step 222 technically is not part of formingthe free layer.

The seed layer may be cooled to below room temperature, via step 224.Step 224 is optional and might be skipped in some embodiments. Whenperformed, step 224 is completed before deposition of the materials thatwill form the free layer.

A CoFeB or Fe layer 122 may be provided, via step 226. In someembodiments, the layer formed in step 226 is a CoFeB layer. A diffusionblocking layer 123 may optionally be provided, via step 228. In otherembodiments, step 228 may be omitted.

The diluted magnetic layer 124 is provided, via step 230. A diffusionblocking layer 125 may optionally be provided, via step 232. In otherembodiments, step 232 may be omitted. If step 228 and/or step 232 isomitted, then for some diluted magnetic alloy layers 124, subsequentanneals may be at a reduced temperature. For example, a FeV dilutedmagnetic layer may be provided in step 230. In some such embodiments,any subsequent anneals may be at temperatures not exceeding threehundred degrees Celsius in order to reduce or prevent diffusion of theV.

An Fe or CoFeB layer 126 may be provided, via step 234. Together, steps226 (if performed), 228 (if performed), 230, 232 (if performed) and 234(if performed) may be viewed as providing at least one of the freelayers 120 and 120′.

A capping layer 132 or 132′ is provided, via step 236. Step 236 mayinclude providing a magnesium oxide layer. Thus, step 236 technically isnot part of forming the free layer. Fabrication of the free layer 120 or120′ may then be completed, via step 238. For example, the edges of thefree layer 120 or 120′ may be defined.

Using the method 220, the free layers 108, 108′, 120 and/or 120′ may befabricated. As a result, a magnetic junction having free layer(s) withimproved switching characteristics may be achieved.

FIG. 8 depicts an exemplary embodiment of a memory 300 that may use oneor more of the magnetic junctions 100, 100′ and/or 100″ and/or othermagnetic junction including a free layer such as the free layer 120and/or 120′. The magnetic memory 300 includes reading/writing columnselect drivers 302 and 306 as well as word line select driver 304. Notethat other and/or different components may be provided. The storageregion of the memory 300 includes magnetic storage cells 310. Eachmagnetic storage cell includes at least one magnetic junction 312 and atleast one selection device 314. In some embodiments, the selectiondevice 314 is a transistor. The magnetic junctions 312 may be one of the100, 100′, 100″ and/or other magnetic junction including the dilutedmagnetic layer within the free layer. Although one magnetic junction 312is shown per cell 310, in other embodiments, another number of magneticjunctions 312 may be provided per cell. As such, the magnetic memory 300may enjoy the benefits described above.

A method and system for providing a magnetic junction and a memoryfabricated using the magnetic junction has been described. The methodand system have been described in accordance with the exemplaryembodiments shown, and one of ordinary skill in the art will readilyrecognize that there could be variations to the embodiments, and anyvariations would be within the spirit and scope of the method andsystem. Accordingly, many modifications may be made by one of ordinaryskill in the art without departing from the spirit and scope of theappended claims.

We claim:
 1. A magnetic junction residing on a substrate and usable in amagnetic device comprising: a pinned layer; a nonmagnetic spacer layer;and a free layer, the free layer being switchable between a plurality ofstable magnetic states when a write current is passed through themagnetic junction, the nonmagnetic spacer layer residing between thepinned layer and the free layer, the free layer having a free layerperpendicular magnetic anisotropy energy greater than a free layerout-of-plane demagnetization energy, the free layer including a dilutedmagnetic layer, the diluted magnetic layer having a perpendicularmagnetic anisotropy energy and an out-of-plane demagnetization energy,the perpendicular magnetic anisotropy being greater than theout-of-plane demagnetization energy, the diluted magnetic layerincluding at least one magnetic material and at least one nonmagneticmaterial, the diluted magnetic layer having an exchange stiffness thatis at least eighty percent of an exchange stiffness for the at least onemagnetic material.
 2. The magnetic junction of claim 1 wherein the atleast one magnetic material includes Fe and the at least one nonmagneticmaterial includes at least one of V, Mo, Cr, Al, Ga, W, Sb, Ge and Sn.3. The magnetic junction of claim 2 wherein the diluted magnetic layerincludes Fe and at least one of at least ten atomic percent and not morethan twenty-five atomic percent V, greater than zero and not more thanfive atomic percent Mo, greater than zero and not more than ten atomicpercent Cr, greater than zero and not more than twenty atomic percentAl, greater than zero and not more than twenty atomic percent Ga,greater than zero and not more than ten atomic percent W, greater thanzero and not more than ten atomic percent Sb, greater than zero and notmore than ten atomic percent Ge and greater than zero and not more thanten atomic percent Sn.
 4. The magnetic junction of claim 2 wherein thediluted magnetic layer consists of Fe—X and wherein X is at least one ofat least ten atomic percent and not more than twenty-five atomic percentV, greater than zero and not more than five atomic percent Mo, greaterthan zero and not more than ten atomic percent Cr, greater than zero andnot more than twenty atomic percent Al, greater than zero and not morethan twenty atomic percent Ga, greater than zero and not more than tenatomic percent W, greater than zero and not more than ten atomic percentSb, greater than zero and not more than ten atomic percent Ge andgreater than zero and not more than ten atomic percent Sn.
 5. Themagnetic junction of claim 1 wherein the free layer also includes atleast one of at least one CoFeB layer and at least one Fe layeradjoining the diluted magnetic layer.
 6. The magnetic junction of claim1 wherein the diluted magnetic layer is Fe_(1-t)V_(t) and wherein t isat least 0.1 and not more than 0.25.
 7. The magnetic junction of claim 1wherein the exchange stiffness that is at least ninety percent of the Feexchange stiffness.
 8. The magnetic junction of claim 1 wherein the freelayer has a thickness of at least twenty Angstroms and not more thanthirty-five Angstroms.
 9. The magnetic junction of claim 8 wherein thediluted magnetic layer has a diluted magnetic layer thickness of atleast twelve Angstroms and not more than twenty-two Angstroms.
 10. Themagnetic junction of claim 1 wherein the nonmagnetic spacer layerincludes MgO and adjoins the free layer.
 11. The magnetic junction ofclaim 1 further comprising: an additional nonmagnetic spacer layer, thefree layer being between the additional nonmagnetic spacer layer and thenonmagnetic spacer layer; and an additional pinned layer, the additionalnonmagnetic spacer layer being between the additional pinned layer andthe free layer.
 12. The magnetic junction of claim 1 wherein the freelayer further includes: at least one diffusion blocker layer adjacent tothe diluted magnetic layer.
 13. A magnetic memory residing on asubstrate and comprising: a plurality of magnetic storage cells, each ofthe plurality of magnetic storage cells including at least one magneticjunction including a pinned layer, a nonmagnetic spacer layer and a freelayer, the free layer being switchable between a plurality of stablemagnetic states when a write current is passed through the magneticjunction, the nonmagnetic spacer layer residing between the pinned layerand the free layer, the free layer having a free layer perpendicularmagnetic anisotropy energy greater than a free layer out-of-planedemagnetization energy, the free layer including a diluted magneticlayer, the diluted magnetic layer having a perpendicular magneticanisotropy energy and an out-of-plane demagnetization energy, theperpendicular magnetic anisotropy being greater than the out-of-planedemagnetization energy, the diluted magnetic layer including at leastone magnetic material and at least one nonmagnetic material, the dilutedmagnetic layer having an exchange stiffness that is at least eightypercent of an exchange stiffness for the at least one magnetic material;a plurality of bit lines coupled with the plurality of magnetic storagecells.
 14. A method for providing magnetic junction residing on asubstrate and usable in a magnetic device, the method comprising:providing a pinned layer; providing a nonmagnetic spacer layer, andproviding a free layer, a free layer, the free layer being switchablebetween a plurality of stable magnetic states when a write current ispassed through the magnetic junction, the nonmagnetic spacer layerresiding between the pinned layer and the free layer, the free layerhaving a free layer perpendicular magnetic anisotropy energy greaterthan a free layer out-of-plane demagnetization energy, the step ofproviding the free layer further including providing a diluted magneticlayer, the diluted magnetic layer having a perpendicular magneticanisotropy energy and an out-of-plane demagnetization energy, theperpendicular magnetic anisotropy being greater than the out-of-planedemagnetization energy, the diluted magnetic layer including at leastone magnetic material and at least one nonmagnetic material, the dilutedmagnetic layer having an exchange stiffness that is at least eightypercent of an exchange stiffness for the at least one magnetic material.15. The method of claim 14 wherein the at least one magnetic materialincludes Fe and the at least one nonmagnetic material includes at leastone of V, Mo, Cr, Al, Ga, W, Sb, Ge and Sn.
 16. The method of claim 15wherein the step of providing the diluted magnetic layer furtherincludes: providing Fe and at least one of at least ten atomic percentand not more than twenty-five atomic percent V, not more than fiveatomic percent Mo, not more than ten atomic percent Cr, not more thantwenty atomic percent Al, not more than ten atomic percent Ga, not morethan four atomic percent W, Sb, Ge and Sn.
 17. The method of claim 15wherein the step of providing the free layer further includes: providingat least one of at least one CoFeB layer and at least one Fe layeradjoining the diluted magnetic layer.
 18. The method of claim 15 whereinthe exchange stiffness that is at least ninety percent of the Feexchange stiffness.
 19. The method of claim 15 wherein the free layerhas a thickness of at least twenty Angstroms and not more thanthirty-five Angstroms.
 20. The method of claim 15 wherein the step ofproviding the free layer further includes: providing at least onediffusion blocker layer adjacent to the diluted magnetic layer.